The present invention relates to an intake manifold for an engine.
Japanese Laid-Open Patent Publication No. 2008-184939 discloses an intake manifold that includes a manifold body. The manifold body is a synthetic resin single component that includes a surge tank and a plurality of inlet pipes. Synthetic resin internal pipes are provided inside the manifold body. Each internal pipe protrudes into the surge tank from the proximal portion of one of the inlet pipes, or from a portion of the inlet pipe that is coupled to the surge tank.
Because of the internal pipes provided separately from the manifold body, the conventional intake manifold has a large number of components and a complicated structure. Omission of the internal pipes would simplify the structure. However, such omission would lower the pressure capacity of portions of the intake manifold including the proximal portions of the inlet pipes. The internal pipes have a function for correcting molding strains, which often occur in the vicinity of the proximal portions of the inlet pipes when a surge tank and inlet pipes are integrally molded with synthetic resin. The omission of the internal pipes would therefore make drawbacks due to molding strains conspicuous.